This invention relates generally to the fields of molecular biology and molecular medicine and more specifically to the identification of phosphoinositide 3-kinase related kinases (PIKKs) involved in cell cycle control and mRNA surveillance pathways.
The mitotic cell cycle is the process by which a cell creates an exact copy of its chromosomes and then segregates each copy into two cells. The sequence of events of the cell cycle is regulated such that cell division does not occur until the cell has completed accurate DNA replication. To ensure that cells pass accurate copies of their genomes on to the next generation, evolution has overlaid the core cell cycle machinery with a series of surveillance pathways termed cell cycle checkpoints. The overall function of these checkpoints is to detect damaged or abnormally structured DNA, and to coordinate cell cycle progression with DNA repair.
Members of the phosphoinositide 3-kinase related kinases (PIKK) family of kinases are involved in cell cycle checkpoints and DNA damage repair. The PIKK family members identified to date express a carboxylterminal domain that displays significant sequence homology to the catalytic domains of phosphoinositide (PI) 3-kinases. Indeed, many, but not all of the PIKKs have been shown to possess protein serine-threonine kinase activities (McMahon et al., Cell 94:363-374 (1998); Vassilev et al., Cell 2:869-875 (1998); Grant et al., Cell 2:863-867 (1998); Hunter, Cell 83:1-4 (1995); Tibbetts and Abraham, Signaling Networks and Cell Cycle: Themolecular Basis of Cancer and Other Diseases pp. 267-301 (2000)). In mammalian cells, three PIKK family members, ATM, ATR, and DNA-dependent protein kinase (DNA-PK), serve as proximal signal transducers in cell-cycle checkpoint and DNA repair pathways (Abraham, Genes & Dev. 15:2177-2196 (2001); Durocher and Jackson, Curr. Opin. Cell Biol. 13:2225-231 (2001)). The critical roles of ATM in orchestrating cellular responses to various forms of stress are underscored by the diverse pathologies associated with the hereditary disorder, ataxiatelangiectasia (A-T) (Crawford, Seminarsin Ped. Neuro. 5:287-294 (1998); Rotman and Shiloh, Human Mol. Gen. 7:1555-1563 (1998); Rotman and Shiloh, Oncogene 18:6135-6144 (1999)). A-T patients lack functional ATM and develop symptoms including extreme sensitivity to irradiation, cerebellar degeneration, oculocutaneous telangiectasias, gonadal deficiencies, immunodeficiencies, and increased risk of cancer (Lehman and Carr, Trends in Genet. 11:375-377 (1995)). Fibroblasts derived from these patients show defects in cell cycle checkpoints and are defective in their response to irradiation (Painter and Young, Proc. Natl. Acad. Sci. (USA) 77:7315-7317 (1980)).
In general, the proteins in the PIKK family of kinases play important roles in mRNA surveillance and cell cycle progression in order to insure genetic integrity from generation to generation. Compounds that modulate PIKK polypeptides can result in altered progression through the cell cycle leading to increased or decreased cell survival. For example, a PIKK-modulatory compound can make a cell more or less susceptible to cell death in the presence of radiation or a cytotoxic agent.
All cancer cells have a dysfunctional cell cycle and continue through the cell cycle in an inappropriate manner, either by failing to respond to negative growth signals or by failing to die in response to the appropriate signal. In addition, most cancer cells lack genomic integrity and often have an increased chromosome count compared to normal cells. Therefore, compounds that inhibit cell cycle checkpoints or DNA damage repair, in combination with the cytotoxic agents, can cause cancer cell death by forcing cancer cells to progress through the cell cycle in the presence of DNA damaging agents such that they undergo events that lead to cell death.
Thus, there exists a need to identify additional members of the PIKK family of kinases and compounds that modulate these kinases. The present invention satisfies this need and provides related advantages as well.